You manipulate sounds waves in a 5-foot-radius sphere centered on yourself to protect against eavesdroppers while allowing those within to converse normally. No sound can pass through the sphere; creatures within are immune to thunder damage from sources originating outside and are effectively defended to everything not within the sphere, and vice versa. Until the spell ends or you dismiss it as a bonus action the sphere moves with you, centered on you.

A successful insight check to read lips can still reveal what's said on the other side of the sphere.

At Higher Levels. When you cast this spell using a spell slot of 5th level or higher, the duration increases by 1 hour for each slot level above 4th.